Moisture-Responsive Natural Fiber Coil-Structured Artificial Muscles

Miniature linear actuators, also known as artificial muscles, mimic the contractile action of skeletal muscles and have potentials in applications, such as soft robotics, prosthetics, exoskeletons, and smart textiles. Natural fibers commonly used in textiles, such as wool, cotton, and flax, are highly anisotropic materials in response to moisture stimulus. Here, we report that this anisotropic property of the natural fibers can be utilized to provide musclelike contractile motions when they are constructed into springlike cylindrical coils by twist insertion. The treatment and conversion of these natural fibers into high-performance musclelike actuators are described. The musclelike actuators made from natural fibers can provide output strain, stress, and work capacity that are orders of magnitude higher than those of animal skeletal muscles and many artificial muscles made from synthetic materials. The natural fiber artificial muscles are demonstrated for potential applications in smart textiles to alleviate body discomfort caused by sweating during sports and other physical activities.